The present invention relates to a device for locking a nut, and more particularly to a device for locking a nut in a tightened position on a rotary shaft.
In order to prevent a nut from loosening after it has been tightened on a rotary shaft, it is common practice to use locking devices. Certain nuts of small size are provided with a so-called “self-locking” device that is normally in the form of a polymer ring adjacent to the tapping of the nut. Nevertheless, such self-locking devices are not normally used with nuts of large size.
Another alternative is to use a locking device that operates by co-operation between a finger and notches. For example, on the CFM-56 turbojet, a nut tightened onto a rotary turbine shaft is locked by a ventilation tube situated inside the rotary shaft. A finger is installed on the ventilation tube and it is received in mutually aligned notches in the nut and in the shaft, thus preventing the nut loosening. The finger is prevented from tilting by the tube being centered at a plurality of locations along its length.
However, such a ventilation tube is not always available. In order to be able nevertheless to achieve reliable locking of a nut of large size, patent application FR 2 978 218 proposes an alternative locking device, enabling a nut to be locked in a tightened position on a hollow rotary shaft, at least one end. That locking device comprises a plurality of outer notches formed in a face of the nut, said outer notches extending parallel to a longitudinal axis of the nut, and a plurality of inner notches formed in the end of the rotary shaft, said inner notches extending parallel to a longitudinal axis of the rotary shaft, together with a ring suitable for being installed inside said end of said rotary shaft and presenting at least one first radial finger that is to be received both in one of the inner notches and also in one of the outer notches, when the nut is in a tightened position and the two notches housing said first radial finger are at least partially in alignment in a radial direction.
On a rotary shaft, it is also important to achieve accurate balancing of all of the parts so as to avoid any unbalance that would lead to vibration, noise, and fatigue. Thus, in the device disclosed in FR 2 978 218, it is proposed to balance the ring with additional fingers that are shorter and that are received only in the inner notches of the rotary shaft. Nevertheless, that solution requires compromises in the design of the device, in particular concerning the positioning and the dimensioning of the notches.